Wave generator



June 21, 1960 e. E. WEIBEL WAVE GENERATOR 2 Sheets-Sheet 1 Filed Feb.12, 1957 I ifiwtt--- INVENTOR GERfi/ARDE. Wf/BEZ &

ATTORNEY June 21, 1960 e. E. WEIBEL WAVE GENERATOR 2 Sheets-Sheet 2Filed Feb. 12, 1957 [06A RITA/MIC FUNCTION PARABOLIC FUNCTIO INVENTORGER/MRO E. WEIBEL ATTORNEY WAVE GENERATOR Gerhard E. Weibel, Manhasset,N.Y., assignor, by mesne assignments, to Sylvania Electric ProductsInc., Wilmington, Del., a corporation of Delaware Filed Feb. 12, 1957,Ser. No. 639,814

4 Claims. (Cl. 315-7) My invention is directed toward wave generators.

In the electronic arts it has become necessary to generate, atrelatively high power levels, electromagnetic waves at wavelengthsshorter than a centimeter; i.e. millimeter and submillimeter waves. 1have invented a device (which I define as a wave generator) that can beused for this purpose.

Accordingly, it is an object of my invention to generate millimeter andsubmillimeter waves at relatively high power levels.

Another object is to provide new methods for generating electromagneticwaves.

Still another object is to provide new types of devices for generatingelectromagnetic waves.

Yet another object is to provide new millimeter and submillimeter wavegenerators which can generate millimeter and submillimeter waves atrelatively high power levels.

A further object is to accelerate electrons in such manner thatsubmillimeter waves are radiated therefrom.

Another object is to compress a large number of electrons into a beamwith diameters comparable or smaller than the wavelength of theradiation to be generated.

Still a further object is to provide new millimeter and submillimeterwave generators in which are incorporated means for acceleratingelectrons in such a manner that millimeter and submillimeter waves areradiated from these electrons.

These and other objects of my invention will either be explained or willbecome appa ent hereinafter.

As is well known to the art, when an electron is accelerated, energy inthe form of electromagnetic waves will be radiated therefrom, theradiated power increasing as the magnitude of the accelerationincreases.

In accordance with the principles of my invention, a plurality ofelectrons in an evacuated region of space are compressed into acylindrical element, the diameter of this element being of the order ofthe wavelength to be generated or smaller, its axial length being muchlarger than its diameter. Stated differently, the electrons arecompressed into an elongated element of relatively short length and verysmall cross section; I define such an element as an electron string orthread.

This string is acted upon by magnetic and electric forces in such mannerthat the ends of the string remain fixed in position and always definethe axis of the undefiected string, which I define as the string axis.The portions of the string intermediate its ends curve radially outwardfrom the string axis. The radial displacement between the string and thestring axis attains a substantially constant maximum value over aselected region of the string (as for example a region centered aboutthe midpoint of the string) and gradually decreases at each side of theselected region.

Further, the string is caused to vibrate in one or more planes about thestring axis in such manner that the path of any point on the string, ina plane conta1ning this point and perpendicular to the string axis, is acynited States Patent cloidal path. Under these conditions, theelectrons the string will be so accelerated as to radiate elect magneticwaves of extremely short wavelength, as for ample submillimeter waves.

More particularly, an electron beam, after emissl from a suitablesource, is accelerated to a high veloc and then passes through anevacuated spacial region ward a collector. A radiation chamberpositioned in t region is interposed in the path of the beam. A m: neticfield is established within the chamber; the magma field vector pointingin a direction parallel to the be: path, and the magnetic fieldintensity attaining a ma mum value over a selected region of the beampath a gradually decreasing along the beam path at each side theselected region. The magnetic field radially co presses the portion ofthe beam; within the chamber.

a result of this compression, a high space charge density establishedwithin the chamber, the space charge dens at any point being determinedby the magnetic field tensity at this point. Due to this charge density,lai potential gradients are established within the chamb As the beamenters the chamber, these gradients act up the beam to reduce the beamvelocity, the velocity in t region of maximum magnetic field intensitybeing i tremely low. As the beam leaves the region of maximt intensity,its velocity increases, and the beam pass through the chamber andtravels toward the collector.

The net effect of the magnetic field compression is t formation of theelectron string previously described the low beam velocity region withinthe chamber, t string axis being parallel and substantially coincidentw; the beam path.

An electric field is also established within the chambt the electricfield vector pointing in a direction perpe dicular to the direction ofmagnetic field vector, the Cit tric field intensity attaining a maximumvalue over least a portion of the selected region of the beam pathagradually decreasing along the beam path at each si of the portion ofthe selected region. The electric fie acts upon the electron string toradially displace ca point on the string (other than the end points of tstring) with respect to the string axis. The rate at whi each point onthe string is radially displaced from t string axis is determined by theelectric field intensi at this point, the ends of the string beingcoincident wi the string axis.

The string, under the influence of both electric a1 magnetic fields, isconstrained to vibrate in one or mo planes about the string axis in apath at which any poi on the string, in a plane containing this pointand pe pendicular to the string axis, traverses a cycloidal pat (Theelectrons in the string are also travelling throu the chamber toward thecollector, but the velocity aloi the path is too small to have anyappreciable effect the motion of the string.)

In one application of my invention, the cycloidal pa of any point on thestring is such that the cusps of 11 path define a straight line whichintersects a normal both the electric field vector and the magneticfield vectt at an acute angle. This type of path is obtained Wilt analternating electric field is used; i.e. the electric fie vectorreverses its direction each half cycle, but alwa remains perpendicularto the string axis.

In a second application, any point on the string describt an epicycloidwhich lies in a plane perpendicular to tl magnetic field vector. Thistype of path is obtained whe the electric field rotates uniformly in aplane perpend cular to the magnetic field vector; the electric field vetor continuously rotates about the string axis in a circ yet remainsperpendicular to the magnetic field vector.

Illustrative embodiments of my invention will now i sesame escribed indetail with reference to the accompanying rawings wherein:

Fig. 1 illustrates the action of a magnetic field upon a action of anelectron beam;

Fig. 2 illustrates the action of mutually orthogonal elecl6 and magneticfields upon a section of an electron earn;

Fig. 3 is a cross sectional view of the path traversed y an. electronstring under the influence of the magnetic nd electric fields of Fig. 2;

Fig. 4 illustrates the curvature of an electron string roiting under theinfluence of mutually orthogonal mageii; and electric fields, theelectric field being a rotating 6 i Fig. 5 is a cross sectional view ofthe path traversed y an electron string under the influence of themagnetic nd electric fields of Fig. 4;

Fig. 6 is a cross sectional view of a tube constructed in ccordance withthe principles of my invention;

Fig. 7 illustrates in enlarged cross section the potential ariaionwithin the radiation chamber of the tube of sg is a view of theradiation chamber of the tube 8- i Fig. 9 shows a modification of theradiation chamber lown in Fig. 8; and

Fig. 10 shows another modification of the radiation aamber shown in Fig.8.

Referring now to Fig. 1, a section 20 of an electron eam having a beamaxis 22 is compressed axially by a tagnetic field having its magneticfield vector B pointlg in a direction parallel to the axis 22. Themagnetic eld intensity attains a substantially constant maximum alueover region p on section 20 and decreases gradually long the axis 22 ateach side of region p. In this exrnple, the intensity variation of themagnetic field is :presented by a fiat topped curve 24.

As will be explained in more detail hereinafter, the mpression effectslows down the electrons in the beam i that, in the region of highmagnetic field intensity, the ectrons are travelling at an extremely lowvelocity and re formed into an electron string 26.

Fig. 2 shows the distribution of an applied electric deection fieldalong the string 26. The electric field E an alternating field, theelectric field vector E reversig its direction every half cycle yetalways parallel to a :lected direction perpendicular to the magneticfield vecr B The amplitude of the electric field intensity as :presentedby curve 28 varies in the same manner as re magnetic field intensity.However, it will be apirent that the fiat portion of curve 24 issubstantially ider than the fiat'portion of curve 28. Under the intenceof the electric field, the electron string is curved, 1e ends of thestring being coincident with the beam ris and hence defining a stringaxis. All points on the ring intermediate its ends are radiallydisplaced from 1e string axis, the radial displacement of each of thesetermediate points being determined by the electric field tensity at saideach point.

Under the combined influence of the electric and mag- :tic fields, thestring is constrained to move about the ring axis in such a manner thatany point on the string, a plane perpendicular to the string axis whichcontains is point, traverses a cycloidal path.

A typical cycloidal path for such a point R is shown Fig. 3. Theelectric field exerts an electric force on e electrons at rest at R insuch a direction that these ectrons start to travel in the direction ofthe field. As e speed of these electrons increases, the magnetic fieldterts an increasing magnetic force on these electrons hich isperpendicular both to the magnetic field vector id to the instantaneousdirection of electron movement. s a result of the influence of both ofthese forces, the ectrons travel in a cycloidal path 30 having cusps P 5P,,.

Since the magnetic force is always exerted at right I ated wave.

angles to the instantaneous direction of electron motion, no energy istransferred between the magnetic field and the electron.

During its first half sector of travel along any arc of path 30, energyis transferred to the electrons from the electric field; during itssecond half of the sector of travel, energy is transferred from theelectrons to the electric field. If the electrons were not to loseenergy through radiation during the traversal of each arc, the energytransfer in the first half sector would equal the energy transfer in thesecond half sector, and the cusps of the path 30 would fall along thedotted line 32 which is perpendicular both to the electric field vectorE and the magnetic field vector B However, since the electrons areconstantly being accelerated, they are constantly radiating energy; thisradiated energy is supplied by the electric field. Hence, the energytransferred from the field to the electrons during the first half sectorof travel exceeds the energy transferred from the electrons to the fieldduring the second half sector of travel by an amount equal to theradiated energy. As a result, the cusps of path 30 do not fall along thedotted line 32 but rather fall along the solid line 34. Line 34intersects line 32 at an acute angle a.

Since the electric field is an alternating field, the electrons eithertravel generally from left to right, as indicated by the solid portionof path 30, or from right to left, as indicated by the dotted portion ofpath 30.

Due to the acceleration of these electrons, energy is radiated in theform of an electromagnetic wave. The wavelength of the radiated wave isinversely proportional to the magnetic field intensity. The tangent ofangle a (the angle between line 34 and line 32 which is perpendicular toboth the electric and magnetic field vectors) is directly proportionalto the magnetic field intensity, and hence is also inverselyproportional to the wavelength of the radi- The power radiated isproportional to the product of square of the electric field intensityand the square of the number of electrons. Hence, the wavelength of theradiated wave decreases as the magnetic field intensity increases, whilethe radiated power increases as the electric field intensity increases.

It will be apparent from a comparison of curves 24 and 28, that theradiated wave has a wavelength deter mined by the maximum value of themagnetic field intensity; in regions where the magnetic field intensityis less than this maximum value, the electric field intensity is so lowthat substantially no radiation is produced. If the flat portion of theelectric field intensity curve 28 is enlarged, the radiated power willincrease, but the radiated wave will be composed of difierentwavelengths (since radiation will be produced in regions where theelectric field intensity is appreciable and the magnetic field intensityis less than its maximum value); in addition the electron string issomewhat distortedand can become somewhat unstable.

The electric field need not be an alternating field but instead can be acircularly polarized field in a plane perpendicular to the magneticfield; i.e. the electric field vector contained in this plane willrotate uniformly, the amplitude of the electric field intensity stillvarying in the manner shown in Fig. 2. Under these conditions, thestring will rotate about the string axis as shown in Fig. 4.

Further, any point on the string, in a plane perpendicular to the stringaxis and containing this point, traverses a cycloidal path, the cusps ofwhich define a circle as shown in Fig. 5, or expressed difierently, anypoint on the string describes an epicycloid.

The frequency of the electric field rotation is adjusted to be muchlower than the frequency of the cycloidal motion. Under theseconditions, the time required for R to travel through one full arc ofthe cycloid is sufficiently short to permit the electric field to betreated as if it were a constant rather than a rotating field. It can beshown that the same wavelength and power considerations apply to themotions shown in Figs. 3 and 5.

In Fig. 5 it will be seen that when the electric field is treated as aconstant, as for example represented by the solid vector E the tangentdrawn through cusp P represented by the solid line 34, intersects line32 (which is perpendicular both to the electric and magnetic fieldvectors) at an angle a; this angle is identical with angle a of Fig. 3.

Fig. 6 shows, in cross section, a tube in which an electron string isproduced in the manner previously indicated. An electron gun 100 and104, for example of the Pierce type, is mounted within an evacuatedenvelope 102 and produces an electron beam which is accelerated to ahigh velocity by an acceleration electrode 110. The cathode portion 100of the gun, the anode portion 104 of the gun and the accelerationelectrode 110 are respectively connected to different points of directpotential 106, 108 and 120. Point 120 is at a much higher positivepotential than point 106, the difference being on the order of 100,000volts. Point 108 is also at a higher positive potential than point 106,the difference being on the order of 1000 volts.

The high velocity beam, after passing electrode 104, passes through afirst cylinder 110, a radiation chamber 112, and a second cylinder 114,to a collector 116. The radiation chamber, which will be described inmore detail hereinafter, includes a third cylinder 118. Cylinders 110,114 and 118 are all connected to the same point 120 of direct potential,the potential difference between points 106 and 120 being, as mentioned,on the order of 100,000 volts.

Collector 116 includes a collector sleeve 121 connected to point 109,and a repeller ring 122 connected to a point of direct potential 124.The potential difference between points 106 and 124 is on the order of100 volts, point 124 being at the lower potential. The potentialdifference between points 106 and 109 is on the order of a few 100volts, point 109 being at the higher potential.

A magnetic field of the type shown in Fig. 1 is established within theradiation chamber 112 by means of a magnet coil 126 circumferentiallymounted about the third cylinder 118.

Due to the axial beam compression within the radiation chamber producedby the interaction of the magnetic field and the electrons in the beam,a sharp potential depression between the beam and the cylinder 118 isestablished as shown in Fig. 7.

The potential profile of this variation is generated by rotating curve126 about the axis of the beam, or stated differently, curve 126 showsthe potential profile in cross section. In the region between thecylinder wall and the beam periphery, curve 126 describes a logarithmicfunction; in the region between the beam periphery and the beam axis,curve 126 describes a parabolic function. For the region of highestmagnetic field intensity, the potential difference is extremely high,for example, on the order of several hundred thousand volts; thepotential difference decreases as the magnetic field intensitydecreases.

This strong potential depression caused by the electron space chargedensity, acts to reduce the velocity of the high velocity electronsflowing through the first cylinder 110; ultimately, the velocity of theelectrons, when formed into the electron string, is so reduced thatthese electrons are practically at standstill. However, as theseelectrons slowly drift along the beam axis and enter regions of lowermagnetic intensity, the space charge density is reduced, and thevelocity of the electrons increases. Consequently, the electrons leavingthe second cylinder 114 have substantially the same velocity as theelectrons entering the first cylinder 110.

As the electrons leave the second cylinder, they are repelled by therepeller ring 122 and strike the collector sleeve 121 with greatlyreduced velocity. (If the velocity were not reduced, the tube wouldstill function in t manner indicated, but the power losses due toheating the sleeve would be extremely high. The reduction velocityeffectively reduces such losses.)

The radiated wave, as shown in Fig. 6, travels throu ring 122 andthrough a window 123, mounted in envelo 102 and transparent to thiswave, to the outside envelope 102. The wave is then guided in known maner by a conventional horn-radiator 125.

An electric field of the type shown in Figs. 2 and is established withinthe chamber by means of two sep rated electrodes 130 and 132 mountedwithin the thil cylinder 118 in the manner shown in Fig. 8, the alternaing voltage V required to produce the field being a plied betweenterminals 131 and 133.

In order to use an electric field of the type describe in Figs. 4 and 5,the arrangement shown in Fig. 8 ca be augmented as shown in Fig. 9 bythe insertion of tvi additional separated electrodes 134 and 136. A firvoltage V, is applied through transformer 68 betwee plates 130 and 132and a second voltage V is applie through transformer 70 between plates134 and 131 Voltages V and V are alternating voltages having tl samefrequency and amplitude but displaced in phase h relative to each other.This apparatus, as is we known to the art, establishes a circularlypolarized elec tric field within the radiation chamber.

Fig. 10 shows a variation of the device shown in Fig. 5 wherein thecylinder and the electrodes 130, 132, 13 and 136 are structurallycombined; in Fig. 10 the cylir der 118 is divided into four segments150, 151, 152 an 153. The direct potential point 108 is applied to asegments. Appropriate alternating voltages are applie to the segments inthe same manner as in Fig. 9, seg ments and 152 being connected aselectrodes 13 and 132 and segments 151 and 153 being connected atelectrodes 134 and 136.

If desired, the cylinder 118 or segments 150, 15] 152 and 153 can beperforated, and if the magnet co: is split into two or more coilsections separated by gap which are in registration with theperforations, the radi ated wave can travel through the perforations toth outside of the envelope 102 in a direction perpendicula to the stringaxis and gap.

While I have shown and pointed out my invention a applied above, it willbe apparent to those skilled in th art that many modifications can bemade within the soup and sphere of my invention as defined in the claimwhich follow.

What is claimed is:

1. In a wave generator, a radiation chamber, a pin rality of electronsmoving in said chamber along a give] path; means to establish a magneticfield within sai( chamber, the magnttic field vector pointing in adirectioi parallel to said path, the magnetic field intensity havin amaximum value over a selected region of said pat] and decreasing alongsaid path on opposite sides of S31( selected region, said magnetic fieldcompressing said mov ing electrons into an electron string having astring axi: parallel to said magnetic field vector; and means to establish an electric deflection field within said chamber, iht electricfield vector pointing in a direction perpendicula to the magnetic fieldvector, the electric field intensity having a maximum value over atleast a portion of sait selected region and decreasing along said pathon oppo site sides of said portion of said selected region, saitelectric field acting upon said string to radially displaci each pointon said string intermediate its ends from sail string axis, the rate atwhich said each point is radially displaced from the string axis beingdetermined by thc electric field intensity at said point, the ends ofsaid string being coincident with the string axis, said string under theinfluence of both fields, being constrained to move about the stringaxis in a path at which any point or aid string, in a planeperpendicular to the string axis nd containing said any point, traversesa cycloidal path.

2. In a wave generator, a radiation chamber, a pluility of electronsmoving in said chamber along a given ath; means to establish a magneticfield within said hamber, the magnetic field vector pointing in adirection arallel to said path, the magnetic field intensity havingmaximum value over a selected region of said path nd decreasing alongsaid path on opposite sides of said :lected region, said magnetic fieldcompressing said movig electrons into an electron string having a stringaxis arallel to said magnetic field vector; and means to estabsh anelectric deflection field within said chamber, the .ectric field vectorpointing in a direction perpendicular the magnetic field vector, theelectric field intensity aving a maximum value over at least a portionof said :lected region and decreasing along said path on oposite sidesof said portion of said selected region, said ectric field acting uponsaid string to radially displace 1ch point on said string intermediateits ends from said ring axis, the rate at which the radial displacementof lid each point occurs being determined by the electric :ld intensityat said point, the ends of said string being incident With the stringaxis, said string under the ifiuence of both fields, being constrainedto move about 1e string axis in a path at which any point on saidstring, 1 a plane perpendicular to the string axis and containig saidany point, traverses a cycloidal path, the elecons of said any pointradiating energy in the form of l electromagnetic wave, the wavelengthof said wave sing inversely proportional to the maximum value of lidmagnetic field intensity, the power of said radiated ave beingapproximately proportional to the product F the square of the number ofelectrons contained in e portion of said electron string contained insaid por- Jn multiplied by the square of the electric deflection eldintensity in said portion.

3. In a Wave generator, a radiation chamber, a plurality E electronsmoving in said chamber along a given path; leans to establish a magneticfield within said chamber, to: magnetic field vector pointing in adirection parallel i said path, the magnetic field intensity having amaxi- .um value over a selected region of said path and deeasing alongsaid path on opposite sides of said selected gion, said magnetic fieldcompressing said moving elecons into an electron string having a stringaxis parallel i said magnetic field vector; and means to establish anternating electric field Within said chamber, the electric 21d vectoralways pointing in a direction perpendicular the magnetic field vector,the electric field intensity wing a maximum value over at least aportion of said =lected region and decreasing along said path on oppo-:e sides of said portion of said selected region, said electric fieldacting upon said string to radially displace each point on said stringintermediate its ends from said string axis, the maximum radialdisplacement of said each point being determined by the amplitude of theelectric field intensity at said point, the ends of said string beingcoincident with the string axis, said string under the influence of bothfields, being constrained to move about the string axis in a path atwhich any point on said string, in a plane perpendicular to the stringaxis and containing said any point, traverses a cycloidal path, thecusps of said path defining a straight line.

4. In a wave generator, a radiation chamber, a plurality of electronsmoving in said chamber along a given path; means to establish a magneticfield within said chamber, the magnetic field vector pointing in adirection parallel to said path, the magnetic field intensity having amaximum value over a selected region of said path and decreasing alongsaid path on opposite sides of said selected point, said magnetic fieldcompressing said movin electrons into an electron string having a stringaxis parallel to said magnetic field vector; and means to establish anelectric circularly polarized field within said chamber, the electricfield vector always pointing in a direction perpendicular to themagnetic field vector, the amplitude of the electric field intensityhaving a maximum value over at least a portion of said selected regionand decreasing along said path on opposite sides of-said selectedregion, said electric field acting upon said string to radially displaceeach point on said string intermediate its ends from said string axis,the radial displacement of said each point being determined by theamplitude of the electric field intensity at said point, the ends ofsaid string being coincident with the string axis, said string under theinfluence of both fields, being constrained to move about the stringaxis in such a manner that any point on said string describes anepicycloid in a plane perpendicular to the string axis.

References Cited in the file of this patent UNITED STATES PATENTS2,158,114 Fritz May 16, 1939 2,233,779 Fritz Mar. 4, 1941 2,306,875Fremlin Dec. 29, 1942 2,404,417 Varela July 23, 1946 2,409,179 AndersonOct. 15, 1946 2,409,608 Anderson Oct. 15, 1946 2,414,121 Pierce Jan. 14,1947 2,424,965 Brillouin Aug. 5, 1947 2,438,954 Towns Apr. 6, 19482,634,372 Salisbury Apr. 7, 1953 2,730,648 Lcrbs Jan. 10, 1956 2,745,039Bowen May 8, 1956

